The major objective of this proposal is to measure, using 2H NMR spectroscopy, how several well-characterized integral-membrane proteins alter the conformation and organization of phospholipid molecules in the bilayer. A multi-order parameter based approach has been developed for analyzing the spectral lines from aqueous dispersions of multiply 2H-labelled phosphatidylcholine. Using molecular order parameters derived from a rigid region of the phosphatidylcholine molecule, it is possible to characterize in greater detail than previously done the nature of the ordering of this region, as well as more flexible sites in the molecule. It will be a goal of this study to extend the approach to describe in detail how proteins and steroids alter bilayer structure in phosphatidylcholines as well as in other phospholipid bilayer systems. Furthermore, we wish to define how several pharmacologically active glucocorticords, such as methylprednisolone used in the treatment of brain and spinal cord injury, alter bilayer structure and the nature of protein-lipid interactions in membranes. It has been proposed that these substances exert their biological activity through an alteration in membrane structure rather than through a receptor-mediated mechanism. Related steroids, which are shown to have the same effect on bilayer structure but without the receptor-mediated glucocorticord side effects will be sought. A second major aim of this proposal is to use 2H NMR to determine the molecular events occuring at the phase transitions of phospholipid bilayer systems, and to show how protein and steroid alter these events. This approach will assist in better defining the nature of protein-phospholipid and steroid-phospholipid interactions in the bilayer. The ultimate goal of such studies is to understand how the lipid environment regulates the activity of proteins associated with biological membranes.